1. Field of the Invention
The present invention relates to a sheet-like medium alignment apparatus, sheet-like medium post-treatment apparatus and image forming apparatus.
2. Description of the Prior Art
A sheet-formed medium alignment apparatus provided with a returning means consisting of a rotating body is known in the prior art, wherein a sheet-formed medium is ejected onto a loading means by an ejecting means and the end of the aforementioned sheet-formed medium on the upstream side in the direction of ejection is pressed against the vertical wall (end fence) provided at the alignment position, whereby the sheet-formed medium is aligned and loaded. External force is applied to the sheet-formed medium ejected onto the aforementioned loading means (tray), and the medium is fed to the aforementioned vertical wall so as to be aligned.
The sheet-like medium handled in the present specification includes duplicating paper, transfer paper, recording paper, cover sheet, offset paper (divider), computer sheets, special paper, OHP sheet and others. In the following description, they will be genetically called sheets.
In an image forming apparatus, a punching unit for punching filing holes on the imaged sheets ejected from the image forming apparatus, staple means, and a sheet-like medium post-treatment apparatus for post-treatment such as stamping, the sheets ejected from the ejecting means are loaded on a tray as a loading means called an ejection tray or loading tray. The sheets loaded on the loading means are automatically aligned for subsequent use. In this case, the major point is the degree of sheet alignment, namely, accuracy of alignment.
In FIG. 77 illustrating an example of the prior art sheet treatment apparatus, for example, sheets S1 with an image created thereon by an image forming apparatus (not illustrated) are fed to the sheet processing apparatus, and are led to a pair of ejection rollers 3 as an ejecting means comprising a lower roller 3a and a upper roller 3b through the ejection sensor for detecting the passage of this sheet. Then sheets are ejected in the direction of ejection “a” (orthogonal to the axial direction of the lower roller 3a within the common tangential plane between a lower roller 3a and a upper roller 3b) on a direct extension of the aforementioned feed direction.
A vertical wall (end fence) 131 is provided below the ejection roller 3, and a tray 12 is located in such a way that it crosses this end fence 131. A tray 12 has a slope which is higher on the downstream side of ejection direction than the fence 131, and sheets are loaded on this slope. Further, tray 12 is movable in the vertical direction, and a sheet surface feeler (not illustrated) detects the top surface of the tray 12 (the top surfaces of the sheets when the sheets are loaded). As sheets are stacked on the tray 12, the tray 12 is lowered, and control is made to ensure that the distance from the nip of an ejection roller to the top surface of the sheet on the tray 12 will be kept constant.
Depending on the ejection speed, the intermediate position of the sheets S1 ejected from the ejection roller 3 to the tray 3 may be bent in the process of ejection while the rear ends of the sheets S1 are still gripped by the ejection roller 3 as shown in FIG. 77, and the sheets S1 may be fed out with the leading edge thereof kept in contact with the loaded sheets S″ which are already loaded on the tray 12.
Under this condition, the leading edges of sheets S1 moves the sheets S2 located on the top surfaces of the loaded sheets S″ toward the downstream side in direction of ejection a; therefore, the trailing edges of the sheets S2 aligned after having been pressed against the end fence 131 by the inclination of the tray 12 are separated from the end fence 131 and is misaligned toward the downstream side in the direction of ejection, with the result that the trailing edge is misaligned.
In the paper copying industry, a bundle of loaded sheets may be fed to the next process to be processed by a punching machine, for example, and this requires excellent alignment accuracy. If a bundle of sheets has a poor alignment accuracy, the bundle taken out of the tray has to be aligned again by human hand before it is fed to the punching machine, with the result that work efficiency is reduced. To solve this problem, the upstream segment, e.g., copying industry requires very severe alignment accuracy of the loaded sheets. Improvement of alignment accuracy is urgently required at present.
To solve this problem of misalignment resulting from the loaded sheet being moved by the leading edge of the ejected paper according to the prior art, a retaining roller 121′ as a retaining means is provided at a central position along the width of the sheet between the ejection roller 3 and the upper surface of the tray 12 in such a way that it can be rotated and driven, as shown in FIG. 78.
The retaining roller 121′ is fixed at a specified position on the immovable member, and is kept in a light contact with the upper surface of the tray 12 (the top surface of the sheet when the sheet is loaded). When paper is loaded on the tray 12, even if the leading edge of the paper ejected on the tray 12 attempts to move the loaded paper, the loaded paper is exposed to the force opposite to the direction of ejection “a” while being pressed by the retaining roller 121′, and is kept pressed against the end fence 131.
The sheet S1 ejected from the ejection roller 3 onto the tray 12 in the manner mentioned above is held by the retaining roller 121′, and is pressed against the end fence 131. This eliminates the so-called vertical misalignment on the trailing edge in the direction of ejection a.
When the retaining roller 121′ is rotating in the arrow-marked direction as shown in FIG. 78, the retaining roller 121′ has also a function of returning the sheet to the side of the end fence 131. The roller in this case is referred to as a returning roller. As shown in FIG. 79, the returning roller 121′ is kept in a light contact with the top surface on the tray 12 and is driven in such a way as to move the contact surface toward the upstream side in the direction of ejection a, so the sheets fed onto the tray 12 whose trailing edges are gripped by the returning roller 121′ are returned opposite to the direction of ejection “a” and are pressed against the end fence 131.
The sheets S1 ejected by the ejection roller 3 and loaded on the tray 12 in the manner mentioned above are gripped by the returning roller 121′. Or those sheets which have been ejected slightly farther in the direction of ejection “a” than the returning roller 121′ are slid under its own weight along the inclination of the tray 12, and their trailing edges are gripped by the returning roller 121′ to be pressed against the end fence 131, whereby the trailing edge is aligned.
These sheets fall under free conditions without any restriction on the distance from the ejection roller 3 to the tray 12, namely, on the distance of free fall of the sheet until they are loaded on the tray 12 by free falling after their trailing edges are released from the ejection roller 3. So a slight displacement will be formed between sheets under the influence of air, and alignment accuracy will be adversely affected. However, these sheets are correctly pressed against the end fence 131 due to the inclination of the tray 12 and the action of the returning roller 121, with the result that basically excellent alignment accuracy is ensured.
Another known art is a sheet-like medium alignment apparatus provided with a sorting means for sorting the sheet-like media fed upward one after another from the image forming apparatus. Such a sheet-like medium alignment apparatus is characterized by operation by an aligning means for aligning the sheet trailing edge, operation by a returning means for returning the sheet to the end fence and sorting operation by the aforementioned sorting means. These operations are performed by using the aforementioned time intervals of sheet-like media being fed one after another.
For example, when the sheet-like medium has been ejected and loaded onto the tray, the following operations are required before the next sheet is ejected; (1) a returning operation for ensuring alignment in the direction of ejection by returning the sheet-like medium with the returning roller until it is pressed against the end fence in order to ensure alignment between the sheet-like medium immediately after ejection and the edge of the already ejected sheet-like medium in the direction of ejection; (2) an alignment operation of gripping the end face in the direction of shift by the aligning means together with the sheet-like medium of the same portion already ejected in order to improve the alignment of the edge of the sheet-like medium in the direction of shift; and (3) a sorting operation by shifting the tray (or an aligning member) by a specified distance only during the time between ejection of the sheet-like medium at the end of this portion and ejection of the first sheet-like medium of the next portion.